GB1593310A

GB1593310A - Rotatable magnetic transducer head

Info

Publication number: GB1593310A
Application number: GB52704/77A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1976-12-22
Filing date: 1977-12-19
Publication date: 1981-07-15
Also published as: ATA953676A; JPS57567B2; DE2755287A1; JPS5380212A; ES465258A1; FR2379128B1; DE2755287B2; AT351797B; FR2379128A1; IT1088722B; US4186480A; DE2755287C3

Description

PATENT SPECIFICATION

Application No 52704/77 ( 11) 1 593 310 ( 22) Filed 19 Dec 1977 Convention Application No 9536/76 ( 32) Filed 22 Dec 1976 in, ( 33) Austria (AT) ( 44) Complete Specification Published 15 Jul 1981 ( 51) INT CL 3 Gli B 5/42 11 5/52 5/008 ( 52) Index at Acceptance G 5 R B 264 B 37 Y B 402 B 55 X B 632 B 665 B 672 B 789 MM ( 54) ROTATABLE MAGNETIC TRANSDUCER HEAD ( 71) We, N V PHILIPS' GLOEILAMPENFABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:

The invention relates to a rotatable magnetic transducer head arrangement for tape recording and/or playback apparatus for signals having a wide frequency spectrum such as video signals, in which at least one magnetic transducer head comprising a magnetic core having parallel major surfaces, a tape contact face and a transducing gap, is positioned on a disc-shaped carrier member with its major surfaces parallel to a reference surface provided on the carrier member and extending at right angles to its axis of rotation The head arrangement may also include more than one magnetic head, the magnetic heads being angularly spaced from one another round the periphery of the carrier member A method of manufacturing such a head arrangement is described, for example, in Austrian Patent Specification No 293,499 For the reliable operation of such a magnetic head arrangement it is of particular importance that the magnetic heads are located accurately in the required positions on the carrier member of the magnetic head arrangement This positioning becomes more important when a track on a record carrier which is to be scanned by the magnetic head(s) is narrow and when adjacent tracks are situated very close to one another on the record carrier.

It is an object of the invention to provide a method of manufacturing a rotatable magnetic head arrangement with which a particularly exact positioning of the magnetic head or heads on the carrier member can be achieved in a simple and reliable manner.

According to the invention, there is provided a method of manufacturing a rotatable magnetic transducer head arrangement for tape recording and/or playback apparatus for signals having a wide frequency spectrum such as video signals, in which at least one magnetic transducer head comprising a magnetic core having parallel major surfaces a tape contact face and a transducing gap, is positioned on a disc-shaped carrier member with its major surfaces parallel to a reference surface provided on the carrier member and extending at right angles to its axis of rotation which comprises: fixing a reference level for the transducing gap of the magnetic head parallel to and at a given distance from said reference surface which reference level defines the centre of the final transducing gap and then symmetrically with respect to said level removing so much material by means of a laser beam machining operation in which a laser beam is directed onto the tape contact face of the magnetic head first from a first one of the major surfaces of the magnetic core and then from a second one of the major surfaces over the whole gap height, such that the width of the gap is reduced to a given size by the formation of two oppositely located recesses in said major surfaces.

Since the final width of the transducing gap is determined only after providing the magnetic head on the carrier member in relation to a given reference level, this method can ensure that the gap of the magnetic head has an accurately determined gap width and position with respect to the reference surface on the carrier member respectively Where several magnetic heads are provided on the carrier member, the transducing gaps of all the magnetic heads can have exactly the same gap widths and positions with respect to the reference sur( 21) ( 31) en 0 \ Lfn 1 593 310 face It has been found that the attenuation in the signal level produced by the magnetic head as a result of the reduction of the width of the transducing gap is not so large as was expected, which is due to the fact that the material removal by means of a laser beam machining operation does not adversely influence the material structure of the workpiece formed by the magnetic circuit as can be the case with some other machining methods, for example a grinding operation.

In an embodiment where at least two magnetic heads are provided on the carrier member at a given angular distance from one another along the periphery of the carrier member, it has proved advantageous when each two adjacent magnetic heads positioned on the carrier member with their transducing gaps in an angled relationship, after which at the height of the reference level the circumferential distance of the two gaps is measured and compared with a given value, and in the case that a difference is found between the measured distance and the given value, a new reference level is fixed by changing the reference level to one in which the measured circumferential distance corresponds to the given value, after which the gaip width of each transducing gap is reduced to a given size symmetrically with respect to said new level by means of said laser bearn machining operation Thus, the magnetic heads may not only comprise transducing gaps having the same gap widths which are positioned at the same distance to the reference surface, but also the position of the transducing gaps around the circumference of the carrier member is exactly fixed It is to be noted that magnetic head arrangements are known of course having magnetic heads whose transducing gaps show mutually opposite azimuthal angles In order to ensure an exact position of the transducing gaps in such known magnetic head arrangements, usually comparatively complicated adjusting devices are required which may not be necessary when using the above-described method of the invention.

In one method of forming the ultimate gap width of the transducing gap it has proved advantageous when the material is removed by forming successive grooves the lengths of which decrease towards the reference level such that a recess having a trapezoidal cross-section is formed The invention further comprises a method of manufacturing a rotatable magnetic transducer head arrangement for tape recording and/or playback apparatus for signals having a wide frequency spectrum such as video signals, in which at least one magnetic transducer head comprising a magnetic core having two parallel major surfaces, a tape contact face and a transducing gap is positioned on a disc-shaped carrier member with its major surfaces parallel to a reference surface provided on the carrier member and extending at right angles to its axis of rotation, which comprises: forming in the area of the transducing gap remote from the tape contact face of the magnetic head by means of a laser beam directed on to the exposed one of the major surfaces of the magnetic core, a recess which reduces the gap height of the transducing gap to a given size.

The invention furthermore relates to a magnetic head arrangement manufactured according to a method of the invention.

Such a magnetic head arrangement may have at least one magnetic head provided on said disc-shaped carrier member and comprise, on its plate-shaped magnetic circuit two oppositely located grooved-shaped recesses which are produced by a laser beam machining operation, the recesses forming boundaries which define the gap width of transducing gap, and fix the gap at a given distance from a reference surface provided on the carrier member In this manner the position of the gap of a magnetic head of such a magnetic head arrangement can be exactly fixed without this requiring separate adjusting means for the magnetic head.

By way of example, particular embodiments of the invention will now be described in greater detail with reference to the accompanying drawings In the drawings:

Figure 1 shows apparatus for carrying out the method of the invention, Figure 2 is a plan view of the transducing gap of a magnetic head looking towards its tape contact face, Figures 3 and 4 show first and second patterns for the relative movement between magnetic head and laser beam for the material removal operation.

Figure 5 is a view of the transducing gaps of two magnetic heads provided on the carrier member of the magnetic head arrangement, Figure 6 is a plan view of a magnetic head provided on a carrier member of the magnetic head arrangement, Figure 7 shows further apparatus for carrying out the method of the invention with which the circumferential position of the transducing gaps of two magnetic heads is determined, Figure 8 shows the microscopic fields of two microscopes used in the apparatus of Figure 7, and, Figure 9 shows a view of the regions of the transducing gaps of two magnetic heads provided on the carrier member of the magnetic head arrangement as a plan view on their tape contact faces.

Figure 1 shows a support plate 1 on which an XY-coordinate table 2 is provided Said 1 593 310 table 2 consists of a base 3 on which a first table part 4 is arranged so as to be movable in the direction of a double arrow 5 A second table part 6 is provided on the table part 4 so as to be movable in a direction at right angles to the arrow 5 In this manner, a point on the table part 6 can be moved to any position in a plane parallel to a major surface 7 of the support plate when the two table parts 4 and 6 are moved in accordance with the X and Y coordinates of the desired position A motor and a position indicator are associated with each of the two table parts 4 and 6 and are connected to a control device so that the two table parts can be moved automatically The corresponding instructions for making such movements may be given to the control device either manually or via a programme control device Table part 6 comprises a bore 8 debouching into a side surface 9 of the table part 6, the side surface 9 thus acts as a reference plane of the XY coordinate table.

A magnetic head arrangement 10 destined for a recording and/or playback apparatus in which it is to be rotatably drivable, comprises a disc-shaped carrier member 11 supported on a shaft 12 Provided on the carrier member 11 are two diametrically oppositely located magnetic transducer heads 13 and 14 which, as shown in Figure 6, comprise a plate-shaped magnetic circuit 15 having a tape contact face 16, a transducing gap 17, a coil window 18 and a coil 19 passing through the coil window 18 The shaft 12 has an annular shoulder 20 whose end face 22 extending at right angles to the axis 21, of rotation of the magnetic head arrangement forms a reference surface The magnetic heads 13 and 14 are provided on the carrier member 11 in a given position with respect to the above reference surface 22, as described for example, in the aforementioned Austrian Patent Specification, so that the magnetic heads in the axial direction of the magnetic head arrangement have a given distance to the reference surface 22 and assume the desired positions both in the radial direction and in the circumferential direction These positions of the magnetic heads 13 and 14 on the carrier member 11 are already comparatively accurate with a view to the nominal position, but in practice not yet sufficiently accurate for times when the magnetic heads are required to scan very narrow tracks which are situated very closely together on the record carrier.

The magnetic head arrangement 10 is now inserted with its shaft 12 in the bore 8 provided in the XY coordinate table 2 on the table part 6, the reference surface 22 on the shoulder 20 of the shaft 12 abutting the reference surface 9 of the table part 6 Thus the magnetic head arrangement 10 is capable of being moved to any position on the support plate 1 by means of the XY coordinate table 2.

A laser device 23 arranged to produce a laser beam 24 is furthermore provided on the support plate 1 Said laser beam 24 leaving the device 23 in a direction parallel to the major surface 7 of the support plate 1 is reflected by means of an optical deflection device 25 in a direction normal to the major surface 7 The optical deflection device 25 forms part of a microscope 26 which has crossed wires in the microscope eyepiece, the point of intersection of these crossed wires being located on the axis of the reflected part of the laser beam A viewer can thus determine the point of impact of the laser beam on an object which is in the path of the beam, and the viewer can also determine the position of the object with respect to the laser beam.

The carrier member 11 having the magnetic heads 13 and 14 is now moved to a given starting position with respect to the laser beam, by means of the XY coordinate table 2, so that a reference level can be fixed for the transducing gaps of the magnetic heads.

Said reference level will be at a distance A from the reference surface 9 of the XY coordinate table and thus a similar distance from the reference surface 22 of the carrier member 11 The distance A is determined by an imaginary plane in which the laser beam lies and which extends parallel to the reference surface 9 The distance A is chosen to be so that the reference level falls essentially in the central area of the transducing gap viewed in the gap width The carrier member 11 on the table part 6 is then rotated by hand within the bore 8 until the transducing gap of a first one of the two magnetic heads coincides with the crossed wires of the microscope 26 Figure 2 shows diagrammatically such a situation for the first magnetic head 13 The crossed wires 27 and 28 of the eyepiece and the line 29 gives the reference level extending at a distance A from the reference surface 22 In this manner a starting position is fixed for the action of the laser beam 30 Since Figure 2 is taken from a direction looking along the axis of the laser beam, the beam 30 now appears as a small dot.

By means of the programme control device for the XY coordinate table a displacement movement therefor is now required to be established which will determine the machining operation of the magnetic head in the region of its transducing gap by means of the laser beam As shown in Figure 3, the XY coordinate table is first moved so that a point 31 on the magnetic head will lie beneath the laser beam from which the machining operation starts This point 31 lies laterally of the transducing gap 1 593 310 17 and it is located at a given distance B from the reference level 29 and such that.

while considering all possible tolerances, it lies at least slightly outside the major surface 32 of the magnetic circuit 15 bounding the transducing gap in the direction of the width.

A meander-like displacement movement for the XY coordinate table is then initiated by means of the programme control device to produce a relative movement of the laser beam with respect to the magnetic head 13 in the direction of the reference level 29.

Starting from the point 31 the points 33, 34, 35 and so on up to points 36 and 37 are traversed successively The meander-like movement occurs over a distance C which lies at a given distance D from the reference level 29 During said meander-like move2 () ment the laser device 23 is energised so that material of the magnetic circuit is removed by means of the laser beam directed on the tape contact face 16 of the magnetic head 13 as soon as said beam has reached the major surface 32 of the magnetic circuit and that so long until at point 37 the machining operation is discontinued In this manner, a groove-shaped recess 38 is formed at the area of the transducing gap 17 starting from the major surface 32 of the magnetic circuit, which recess reduces the width of the gap 17 with respect to the reference level 29 to the given size D; see also Figure 5 The energy of the laser beam and the relative movement of the magnetic head with respect to the laser beam are matched to each other so that so much material of the magnetic circuit is removed and the groove-shaped recess extends over the whole gap height, so that the recess 38 at its end remote from the tape contact face 16 is partly bounded by a wall 39 of the magnetic circuit, as is shown in Figures 5 and 6 The coil 19 is not shown in Figure 5 to avoid complexity of the drawing.

As shown in Figure 3 the meander-like relative movement between the magnetic head and the laser beam is controlled so that the sections extending parallel to the major surface 32 of the magnetic circuit become shorter and shorter according as they are situated closer to the reference level 29 In this manner a groove-shaped recess is obtained having a trapezoidal cross-section narrowing towards the reference level 29.

Such a cross profile has proved to be particularly advantageous in practice Of course, it would also be possible alternatively to form the groove-like recess with a different cross profile, for example, a rectangular profile or a profile in the form of a segment of a circle.

Figure 4 shows another possibility for the control of the relative movement between the magnetic head and the laser beam, in which the laser beam directly traverses the points 31, 36, 37 to 33 as a result of which a cut is formed which separates the material to be removed from the magnetic circuit which, as a result of the amount of material which is only small when the point 33 is reached is detached from the magnetic circuit Such a control results in a particularly short machining time.

After the above-described machining process to form the groove-shaped recess 38, a further point 40 for the laser beam shown in Figure 2 is adjusted by means of the control device for the XY coordinate table, which position, analogous to the point 31 lies again laterally of the transducing gap 17 at a given distance B with respect to the reference level 29 but is now situated laterally of the major surface 41 of the magnetic circuit opposite to the major surface 32 By means of the control device for the XY coordinate table, again a meander-like relative movement between the magnetic head and the laser beam is produced and the laser device 23 is energised The meander-like movement again occurs over a distance C in the direction of reference level 29, as a result of which the laser beam, starting from the major surface 41 of the magnetic circuit, forms a groove-shaped recess 42 while removing material, which recess, when the distance C is reached, reduces the gap width of the transducing gap with respect to the reference level 29 to the given distance D.

In this manner, the two recesses 38 and 42 limit the transducing gap to a width of exactly 2 D, the centre of the gap being fixed by the reference level 29 lying at the given distance A from the reference surface 22 on the carrier member 11 Thus, the position of the transducing gap for the magnetic head 13 is exactly fixed both as regards its width and its distance from the reference surface on the carrier member.

The XY coordinate table is then again moved to its initial position and the carrier member 11 is rotated by hand within the bore 8 until the transducing gap 17 of the second magnetic head 14 coincides with the crossed wires 27, 28 of the microscope 26.

Thus the laser beam 30 is again positioned with respect to the transducing gap 17 of the magnetic head 14 which lies again in the same reference level 29 as that already used for the first magnetic head 13 By means of the programme control device for the XY coordinate table, in an analogous manner starting first from a point 31 and then from a point 40 groove-like recesses 43 and 44 are formed at the area of the transducing gap, which recesses are situated opposite to each other and now start from the major surface and then from the major surface 46 of the magnetic circuit of the magnetic head 14, as shown in Figure 5 Thus, the transducing gap of the second magnetic head 14 is also 1 593 310 limited to a width of exactly 2 D, the reference level 29 again fixing the centre of the transducing gap.

Thus it is achieved that the transducing gaps of the two magnetic heads 13 and 14 are exactly the same gap width 2 D and their centres are situated on one and the same reference level 29, with which the two transducing gaps also have the same distance to the reference surface 22 on the carrier 11 and the boundaries of the gap width formed by the groove-shaped recesses, viewed in the circumferential direction of the support, are in alignment as shown in Figure 5 In this manner, tolerances which arise during the provision of the magnetic heads 13 and 14 on the carrier member 11 with respect to the distance A of the reference surface 22 on the carrier member 11 are fully compensated for by the formation of the transducing gaps with reduced gap width on the magnetic heads already provided on the carrier member This may be recognized by the fact that the recess 42 in the first magnetic head 13 is deeper than the recess 44 in the second magnetic head 14 and the recess 38 in the first magnetic head 13 is less deep than the recess 43 in the second magnetic head 14, respectively, it being assumed that the first magnetic head 13 after assembly on the carrier member 11 has a slightly smaller distance to the reference surface 42 on the carrier member 11 than the second magnetic head 14 Use of the method of the invention thus enables the gap widths of the transducing gaps and their positions with respect to the reference surface on the carrier to be fixed exactly for both magnetic heads.

Following the machining of the gap width of the transducing gaps, the gap height thereof is advantageously also brought to a given size For this purpose, a recess widening the coil window 18 is formed by material removal by means of a second laser device 47 having a laser beam which is directed onto the major surface of the magnetic circuit, as is shown in Figure 6 by the broken lines 48 As shown, said recess limits the gap height to the distance E In this manner, both magnetic heads 13 and 14 obtain the same gap height, which, together with the same gap width, produces very uniform signal levels from the heads Of course it is also possible for these machining operations to use the same device as for providing the groove-shaped recesses to limit the gap width of the transducing gaps when the XY coordinate table is adapted so that the carrier member with the magnetic heads can be provided on said table in the position corresponding hereto, in which the major surfaces of the magnetic circuits of the magnetic heads must extend at right angles to the laser beam The corresponding relative movement between magnetic head and laser beam may then be produced again by a programme control device for the XY coordinate table starting from an initial position which is determined, for example, by means of a template.

The method of the invention will now be described with reference to an example, in which two magnetic heads are provided on the carrier member of the magnetic head arrangement at an angular distance from each other deviating, for example, slightly from 180 viewed along the axis of the carrier member, the magnetic heads mutually having opposite azimuthal angles of the transducing gap What is important in such a magnetic head arrangement is not only that the transducing gaps of the two magnetic heads have the same gap width and lie at the same reference level with respect to a reference surface, but also that the angular distance from one transducing gap to the other is exactly maintained This can also be achieved by means of a method according to the invention Starting point is again a magnetic head arrangement as already described in which the transducing gaps are provided in the given positions on the carrier member 11 of the magnetic head arrangement 10 having a reference surface 22 and mutually opposite azimuthal angles of the magnetic heads 13 and 14, for example, according to a method described in the aforementioned Austrian Patent Specification in which positions, however, may not have been maintained sufficiently accurately by the usual engineering tolerances.

For carrying out the method, the apparatus of Figure 7 may be used which comprises a support plate 49 on which a cylindrical support 50 is provided having an axial bore 51 which debouchs into an end face 52 serving as a reference surface parallel to the surface of the support plate 49 The shaft 12 of the carrier member 11 of the magnetic head arrangement 10 is inserted into said bore 51, the reference surface 22 of the carrier member abutting the end face 52 In this manner, the two magnetic heads 13 and 14 already provided on the carrier member 11 extend in a plane parallel to the end face 52.

The apparatus of Figure 7 furthermore comprises an optical device consisting of two microscopes 53 and 54 having eyepieces with crossed wires and being provided on the support plate 49 and adjusted in such manner as to be aligned radially to the axis 21 of the carrier member 11 The points of intersection of the eyepiece crossed wires are situated at a given distance A from the end face 52 of the support 50 abutting the reference surface 22 The angular distances of the microscopes with respect to the axis 21 of the carrier member 11 correspond to 1 593 310 that of the desired angular distances of the transducing gaps of the two magnetic heads.

The adjustment of the two microscopes is advantageously carried out with a corresponding template By the distance A again a reference level is fixed which is chosen to be so that, with the carrier member inserted in the apparatus, it falls substantially in the central region of the transducing gaps of the magnetic heads viewed in the gap width.

Figure 8 is a combination of the views seen in the two microscope eyepieces On the left hand side, Figure 8 shows the field of view 55 of the microscope 53 and on the right hand side the field of view 56 of the microscope 54 Both microscope eyepieces have two pairs of crossed wires, namely one pair consisting of the wires 57 and 58 and the other pair consisting of the wires 59 and 60.

In the Figure, a line 61 is drawn through the points of intersection of the two pairs of cross wires which line 61 determines the distance A to the reference surface 22 and hence the reference level The crossed wire pairs are further constructed so that the wires 57 and 58 enclose an angle -a and the wires 59 and 60 enclose an angle +a, the size of the angle a corresponding to the azimuthal angle of the transducing gaps of the magnetic head The reticule formed by the lines 57 and 58 is associated with the microscope 53 and the reticule formed by the lines 59 and 60 is associated with the microscope 54 As a result of the above adjustment of the microscopes 53 and 54 with respect to the given angular distance one reticule 57, 58 corresponds to the desired accurate position of the transducing gap of one magnetic head and the reticule 59 and 6 t) corresponds to the desired accurate position of the transducing gap of the other magnetic head The distance denoted in Figure 8 by F between the points of intersection of the two reticules thus corresponds to the circumferential distance, corresponding to the given angular distance, of the transducing gaps of the two magnetic heads in the reference level The provision of each time two reticules permits of a simple control and adjustment, respectively, of the optical device by a conversion method.

After inserting the carrier member 11 with the magnetic heads 13 and 14 provided thereon into the apparatus, the carrier member 11 is rotated by hand within the bore 51 until the magnetic head comprising one azimuthal angle a for example the first magnetic head 13, is moved in front of the microscope 53 and the transducing gap 17 thereof is made to coincide with the crossing point of wire 57 of the eyepiece, as is shown in Figure 8 The transducing gap 17 of the second magnetic head 14 then appears in the field of view of the microscope 54 with the azimuthal angle +a.

When the two transducing gaps of themagnetic heads 13 and 14 in the reference level A comprise the given nominal value for the angular distance, the transducing gap 17 of the second magnetic head 14 coincides with the crossing point of wire 60 of the relevant eyepiece In the embodiment described it has been assumed that the angular distance of the two transducing gaps in the reference level A is excessive Accordingly, as shown in Figure 8, the transducing gap 17 of the second magnetic head 14 is situated to the right of the wire 60, which means that the circumferential distance in the reference level exceeds the nominal value F by an amount G The amount of G can be read directly by means of a scale 62 provided alongside the wires 59, 60 on the line 61 By moving the reference level A it is now possible to fix such a reference level that the circumferential distance between the two transducing gaps corresponds exactly to the given nominal value F A direct measure of the required displacement of the reference level can be calculated from the value of G together with the azimuthal angle a As shown in Figure 8, a displacement of the reference level to the value A, is required in order that in this new reference level the circumferential distance between the two transducing gaps corresponds to the value F.

The magnetic head arrangement measured in this manner is now inserted in the apparatus of Figure 1 and the initial position for the XY coordinate table is adjusted so that a distance A 1 exists between reference surface 9 and the laser beam directed on the support plate 1 Herewith, the reference level for the magnetic head arrangement is fixed at A 1 The two magnetic heads 13 and 14 are then machined successively in the region of their transducing gaps by means of the laser beam directed on the tape contact face in accordance with a given programme for the relative movement between magnetic head and laser beam, in such manner that groove-shaped recesses are again formed which bound the gap width of the two transducing gaps to a given value of 2 D, entirely analogous as explained in the preceding example, in which in this case, however, the reference level for the individual machining steps is A 1 The proportions in question are shown in Figure 9.

As a result of this it is achieved that at the reference level A, the circumferential distance of the transducing gaps of the two magnetic heads 13 and 14 exactly corresponds to the nominal value F, with which, as desired, the transducing gaps are situated at the given angular distance from each other.

In addition, both transducing gaps have the same gap width 2 D and boundaries of the transducing gaps by the provided grooveshaped recesses 38 and 42 and 43 and 44, 1 593 310 respectively, are in exact alignment in the circumferential direction of the carrier since the centres of the two transducing gaps are fixed by the reference level A, A magnetic head arrangement manufactured in this manner can thus fulfil most accurately the requirements imposed thereon.

When in another magnetic head arrangement a different value G for the circumferential distance of the transducing gaps is measured, the method is carried out entirely analogously For this magnetic head arrangement, the value for the reference level of the machining by means of the laser beam corresponding to the relevant value G is to be used as a base.

Of course, for carrying out the abovedescribed method it is alternatively possible to combine the two pieces of apparatus depicted in Figures 1 and 7 to form a single apparatus Of course, it would also be possible alternatively to produce the relative movement between the magnetic head and the laser beam in such manner that the laser beam is deflected accordingly and the magnetic head is fixed during the machining operation.

Claims

WHAT WE CLAIM IS:-

1 A method of manufacturing a rotatable magnetic transducer head arrangement for tape recording and/or playback apparatus for signals having a wide frequency spectrum such as video signals, in which at least one magnetic transducer head comprising a magnetic core having parallel major surfaces, a tape contact face and a transducing gap, is positioned on a disc-shaped carrier member with its major surfaces parallel to a reference surface provided on the carrier member and extending at right angles to its axis of rotation, which comprises: fixing a reference level for the transducing gap of the magnetic head parallel to and at a given distance from said reference surface which reference level defines the centre of the final transducing gap and then symmetrically with respect to this level removing so much material by means of a laser beam machining operation in which a laser beam is directed onto the tape contact face of the magnetic head first from a first one of the major surfaces of the magnetic core and then from a second one of the major surfaces over the whole gap height, such that the width of the gap is reduced to a given size by the formation of two oppositely located recesses in said major surfaces.

2 A method as claimed in Claim 1, in which at least two magnetic heads are provided on the carrier member at a given angular distance from one another along a periphery of the carrier member, wherein each two adjacent magnetic heads are positioned on the carrier member with their transducing gaps in an angled relationship, after which at the height of the reference level the circumferential distance of the two gaps is measured and compared with a given value, and in the case that a different is found between the measured distance and the given value, a new reference level is fixed by changing the reference level to one in which the measured circumferential distance corresponds to the given value, after which the gap width of each transducing gap is reduced to a given size symmetrically with respect to said new level by means of said laser beam machining operation.

3 A method as claimed in Claim 1 or 2, in which the material is removed by forming successive grooves the lengths of which decrease towards the reference level such that a recess having a trapezoidal crosssection is formed.

4 A method of manufacturing a rotatable magnetic transducer head arrangement for tape recording and/or playback apparatus for signals having a wide frequency spectrum such as video signals, in which at least one magnetic transducer head comprising a magnetic core having two parallel major surfaces, a tape contact face and a transducing gap, is positioned on a discshaped carrier member with its major surfaces parallel to a reference surface provided on the carrier member and extending at right angles to its axis of rotation, which comprises: forming in the area of the transducing gap remote from the tape contact face of the magnetic head by means of a laser beam directed on to the exposed one of the major surfaces of the magnetic core, a recess which reduces the gap height of the transducing gap to a given size.

A method of manufacturing a rotatable magnetic transducer head arrangement, substantially as hereinbefore described with reference to the accompanying drawings.

6 A rotatable magnetic transducer head arrangement, when manufactured by a method as claimed in any one of the preceding claims.

R J BOXALL, Chartered Patent Agent, Mullard House, Torrington Place, London WC 1 E 7 HD.

Agent for the Applicants.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1981.

Published by The Patent Office, 25 Southampton Buildings, London WC 2 A l AY, from which copies may be obtained.